This invention concerns the provision of dispersing agents and their use. In particular it concerns dispersing agents for use in processing particulate solid materials for use as fillers and pigments to be incorporated into sheet materials which are to be brought into contact with foodstuffs.
Particulate solid materials for use as fillers and pigments in sheet materials are commonly prepared for use in suspension in water or an aqueous medium. Operations which are required to render a particulate solid material suitable for these purposes include grinding to increase the particle fineness of the product, and particle size classification to select a product with the range of particle sizes which is most suitable for its desired application. These operations are often most conveniently and efficiently carried out when the particulate material is in suspension in an aqueous medium. However, if these operations are to be successfully performed, it is necessary to ensure that individual particles of the particulate material are not attracted together by electrostatic charges, to form aggregates or agglomerates of particles. For this purpose a dispersing agent is added to the aqueous medium in which the operations are performed, in order to confer a substantially uniform electric charge of the same polarity on the whole of the exposed surface of the particles. In this way the individual particles repel one another, and the formation of aggregates is substantially avoided.
A class of dispersing agents which has been found to be especially suitable for use in processing particulate solid materials in suspension in an aqueous medium is that of the anionic polyelectrolytes, and, in particular, water soluble salts of poly(acrylic acid), such as sodium or ammonium polyacrylate. These polyacrylates generally have a relatively low molecular weight; for example their weight average molecular weight is generally less than 20,000, and preferably less than 10,000.
The United States Food and Drug Administration has imposed an upper limit of 0.25% by weight, based on the weight of the dry particulate material, for the amount of a sodium polyacrylate dispersing agent to be used in the processing of a particulate material destined for use as a filler or pigment in a sheet material which will be brought into contact with certain categories of foodstuffs.
Unfortunately, such a low upper limit restricts the usefulness of polyacrylates for dispersion of materials for incorporation in food grade packaging.
Various species of water soluble chemicals are known in the prior art for use as dispersing agents. The purpose of the present invention is to provide a composition, not disclosed or suggested in the prior art, effective as a dispersing agent in the dispersion of fine particulate material for incorporation in food grade packaging.